According to a new study, more farmworkers are getting infected with bird flu virus than the official numbers reported, raising concerns about the undetected cases.

Published in the U.S. Centers for Disease Control and Prevention's Morbidity and Mortality Weekly, the report found that seven percent of the farmworkers got themselves infected with the virus, which transmitted to them from the infected cows.

The study analyzed blood samples of 115 farmers, who had been exposed to infected cows in Colorado and Michigan. The samples were collected from June to August.

Of the total samples, 8 tested positive for H5 avian influenza antibodies. Only four of them experienced mild symptoms, such as conjunctivitis, fever, runny nose, sore throat, sneezing and diarrhea.

All the affected workers were involved in working close to the cows. Despite being aware that the cows were infected, they did not use of any recommended personal protective equipment.

Earlier, the CDC mandated testing of workers who experienced symptoms after exposure to infected cows. However, now the agency recommends testing for all the workers on farms with infected cows.

Also, the officials are recommending antiviral medication Tamiflu to asymptomatic workers with high-risk exposure, who did not use proper PPE.

"Simply put, the less room we give this virus to run, the fewer chances it has to cause harm or to change," CDC Principal Deputy Director Dr. Nirav Shah said.

"And the best way to limit the virus's room to run is to test, identify, treat and isolate as many cases as possible in humans and as quickly as possible."

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